Single seal with resilient member

ABSTRACT

The invention relates to a single seal, and more specifically to a seal for a rotary shaft extending through a wall, e.g. that of a pump housing. The single seal exhibits one single sealing location between a stationary and a rotating sealing ring. The seal is attached by means of a flange ( 12 ) on to the wall in order to seal off a chamber inside the wall against the shaft ( 22 ) and towards the exterior. According to the invention, the sealing rings ( 1, 2 ) are biased against each other by means of an axially movable member ( 5 ) extending through the wall in order to increase the contact between the sealing rings ( 1, 2 ). The resilient member may be a slitted sleeve ( 5 ) or a coil spring.

FIELD OF THE INVENTION

The present invention relates to a single seal with a resilient memberand more particularly a sealing for a rotating shaft passing through awall, e.g. a pump housing. The single seal has one single sealinginterface between a stationary and a rotating sealing ring. The sealingrings are biased towards each other by means of an axially extending,resilient member extending through the wall. The resilient member isarranged outside the pumped medium.

STATE OF THE ART

In this context it is previously known to use springs to keep sealingcartridges together. One arrangement is shown e.g. in U.S. Pat. No.2,158,832. A problem with this arrangement is that the springs arearranged inside the pump housing, i.e. in the pumped medium. The springassembly is bulky, and therefore may not be arranged in limited spaces.When pumping liquid media, especially liquid foodstuffs, there will alsobe problems in that the pumped medium blocks the spring movement. Thespring assembly also has a lot of gaps in which the pumped medium may becollected, resulting in hygienic problems.

From SE 9803436-6 it is known to arrange the springs outside the pumpedmedium. Here a single seal has an outer sealing ring and an innersealing ring in sliding and sealing contact with each other. The outersealing ring is attached to the flange, and the inner sealing ring isattached to an axially movable sleeve. The sleeve in turn is attached toand is rotating with the shaft and is extending through the wall and theflange. The seal also has a spring assembly arranged outside the walland provides a force to increase the contact between the sealing rings.

A problem with this seal is that it is composed of a relatively largenumber of parts, such as coil springs and driving pins and specialfastening means therefor. It is desirable to be able to provide a sealhaving the same function but having fewer parts and thus a simplerassembly. Also, a rigid sleeve does not follow the movements of theshaft.

The present invention solves these problems by means of a new design ofthe single seal. The sealing rings are biased towards each other bymeans of an axially displaceable, resilient member extending through thewall. The resilient member is arranged outside the pumped medium.

One advantage is that one single member both provides the biasing forcekeeping the seal package together and biasing the sealing rings towardseach other, and in addition transfers the rotation of the shaft to oneof the sealing rings. The number of parts of the seal is decreased andthe assembly of the seal is simplified. Since the member is resilient,it is also capable of accommodating any movements of the shaft incontrast to a rigid sleeve.

The seal is also substantially free from pockets, in which medium maycollect. The whole spring package is arranged on the atmospheric side,so that the problems associated with the pumped medium in contact withthe springs are avoided.

SUMMARY OF THE INVENTION

Thus, the present invention provides a single seal for sealing of arotating shaft extending through a wall. The seal is mounted on the wallby means of a flange in order to seal off a chamber inside the wallagainst the shaft and towards the exterior. The seal comprises an outersealing ring and an inner sealing ring, said sealing rings being insliding and sealing contact with each other. The outer sealing ring isfastened to the flange and the inner sealing ring is fastened to anaxially extending member, and in turn fastened to and rotating togetherwith the shaft and is extending through the wall and the flange.

According to the invention, the axially extending member is resilientand provides the force acting in a direction to increase the contactbetween the sealing rings.

In one embodiment the resilient member is a slitted sleeve.

In another embodiment the resilient member is a coil spring.

The invention is defined in the accompanying claim 1, whereasadvantageous embodiments are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail hereinafter, with reference tothe enclosed drawings, of which:

FIG. 1 is a cross sectional view of a single seal according to a firstembodiment of the invention along the cross-section in FIG. 3;

FIG. 2 is an end view of the seal mounted on a flange,

FIG. 3 is a cross-sectional perspective view of the single seal of FIG.1,

FIG. 4 is a cross-sectional perspective view of a resilient member inthe form of a slitted sleeve,

FIG. 5 is a cross-sectional view of a single seal according to a secondembodiment of the invention having a resilient member in the form of acoil spring,

FIG. 6 is a sectional perspective view of a resilient member in the formof another slitted sleeve,

FIG. 7 is a plan view of a piece cut-out from a metal sheet for formingthe sleeve of FIG. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to a single seal, especially suited foruse in a pump for foodstuffs and similar. The hygiene requirements forsuch pumps are very stringent, entailing that the sealing package mustbe as smooth as possible, in order for the foodstuff pumped not tocollect in pockets and minor spaces. Inside such pumps, often the roomfor the seal is also limited. Often the sealing function has beenprovided by box plaits with a cross section of 9×9 mm. The foodstuffsare also generally pumped under low pressure, requiring a high degree ofbalancing of the seal.

The present invention provides a single seal, well fulfilling the abovedemands thanks to a novel design.

Generally, the sleeve is delivered as a cartridge or package to befastened to a wall (not shown) around a pump shaft 22, such as shown inFIGS. 1 and 3. The package is fastened by means of screws through aflange 12. In FIG. 1, the pump chamber is located to the left of theflange 12. In the pump chamber is a pump runner (not shown) propellingthe pumped medium. In the present description, the terms outer and innerrelate to positions with respect to the pump chamber and the outside ofthe flange. In other words, outer is to the right in the figures andinner is to the left in the figures. In FIG. 2, two notches or recesses21 are shown, in which screws are placed for fastening the seal to thewall of the pump housing.

As mentioned earlier, the invention relates to a single seal, i.e. thereis only one sealing interface between moving parts. The seal has acounter sealing ring or outer sealing ring 1 (inside the pump housing)and an inner sealing ring 2. The outer sealing ring 1 is located in arecess in the flange 12. In an alternative, the sealing ring 1 may beheld by a retaining ring. Between the outer retaining ring 19 and theflange there is further a rubber seal in the form of a sealing sleeve11. Between the flange 12 and the pump house wall (not shown) there isfurthermore a flat seal 16.

The inner sealing ring 2 thus rotates with the shaft 22. It is held by aresilient member, here an axial through sleeve 5. The sleeve holds thesealing ring 2, e.g. by means of lugs 15 at the edge of the sleeve, thelugs engaging a recess in the sealing ring 2.

The lugs 15 are most clearly shown in FIG. 4, only showing the sleeve 5.The lugs 15 are formed by tongues slitted and bent from the sleevematerial. At the assembly of the sleeve in the sealing ring 2, the lugsare engaged by a pair of tongs and moved resiliently together so thatthey can pass into the sealing ring 2 and are then released outwardsinto their respective recesses.

It is this sleeve 5 that rotates the inner sealing ring 2. The sleeve 5transfers a torque acting in a direction to drive the inner sealing ring2 together with the shaft 22. The sleeve is driven in turn by a couplingon the outside (the atmospheric side) of the pump housing. In itssimplest form, the coupling is one or more radial stop screws 4 that aresecurely tightened against the shaft 22. The sleeve 5 is extended up toa desired biasing force before the stop screws 4 are tightened.

The sleeve 5 also provides the resilient force keeping the sealing rings1, 2 against each other. The sleeve has been made resilient by forming anumber of slits 6 and circular segments 13. The segments 13 areconnected to each other by leaving lands 14 of the sleeve material. Thelands 14 are alternately located, such that the sleeve may be extendedelastically like a spring. Suitably, there are two lands 14 between eachsegment 13. In that case, the lands are located opposite each other by180° in a pair with 90° to the lands in alternate pairs. If a stifferresilience is desired more lands per pair may be used. It will beappreciated that the lands should be distributed evenly around thecircumference and alternately in every second pair.

The number of segments, as well as the axial width of the segments andthe lands and the circumferential extension of the lands may be variedin order to obtain the suitable resilient characteristics.

Suitably, the sleeve is manufactured from stainless steel with asuitable coefficient of elasticity, e.g. a spring steel.

Another embodiment of the resilient sleeve 5′ is shown in FIGS. 6 and 7.The lugs 15 are replaced by crescent shaped anchoring hooks 15′. In thisembodiment, the segments 13′ and slits 6′ are more oval and have roundededges towards the lands 14′. Thus, straight corners are avoided whichotherwise can cause unnecessary stress in the material. Also, the sleeve5′ has a uniform thickness associated with a preferred manufacturingmethod as described below.

A preferred manufacturing method comprises laser cutting the shape, i.e.the outer contour of the intended sleeve 5′ as well as the slits 6′,from a rolled metal sheet, roller bending the cut-out piece into thefinal circular shape, and welding the axial edges together. The hooks15′ are bent outwards 900 (not shown) to be able to engage grooves inthe sealing ring. This manufacturing method is economic and results insuperior resilience characteristics.

The sleeve may also be manufactured by drawing from a steel cylinder.Alternatively, the sleeve may be forged from a cast tube or bored barand the slits milled away.

The choice of material as well as the selected manufacturing methodaffects the resilient characteristics of the finished sleeve.

As an alternative to a resilient sleeve, a coil spring 8 may be used asis shown in FIG. 5. The inner end of the coil spring 8 is attached tothe retainer ring 18 in turn retaining the inner sealing ring 2′. Theretaining ring may also be integral with the sealing ring as in FIG. 1.The retaining ring 18 is provided with an internal groove following thepitch of the spring (unbiased or somewhat biased). The spring 8 isthreaded in the groove and ends with a straight axially directed part 9engaging a recess 19 in the retaining ring 18. The outer edge of thecoil spring 8 is correspondingly attached to an outer retaining ring 17by a straight axially directed part 10 engaging a recess 7. One or morestop screws 20 are tightened against the shaft to secure the outerretaining ring 17 and thereby transmitting the rotation of the shaft tothe inner sealing ring 2′ via the spring 8.

A disadvantage compared to the sleeve is that the coil spring is notindependent of the direction of the rotation. The shaft should be drivenin that direction tending to retract the coil spring radially andaxially. If the shaft is driven in the other direction, the coil springwill rise radially which can cause a break. However, the coil springprovides a cheaper and good functional alternative in some applications.In other respects, the function of this embodiment does not differ fromthe embodiment with the resilient sleeve.

Because the spring arrangement and the coupling are located outside thepump housing on the atmospheric side, the edge width of the sealingpackage inside the pump housing can be kept small.

The resilient sleeve 5, 5′ (or the spring 8) provides a force pullingthe inner sealing ring 2 (or 2′) towards the outer sealing ring 1. Theforce from the sleeve acts to press the sealing rings 1, 2 (or 2′)against each other. The force is a complement to the hydraulic pressureinside the pump, which also acts in the same direction. However, beforethe pump starts, there is no overpressure in the pump housing.

When the pump is operated with for example foodstuffs, low pressures aregenerally used, e.g. 6 bar. In order to obtain a secure sealingfunction, a high degree of balancing is thus required of the sealingpackage. The balancing degree is the quotient between the area actedupon by the hydraulic pressure and the sealing area. In spite of thepresent single seal having a relatively low edge width, about 9 mmbetween its inner and outer diameters, the single seal has a balancingdegree of about 1.3.

The seal also has few corners and areas where the pumped medium couldcollect and eventually cause bacteria colonies to develop when the pumpis used for pumping foodstuffs.

The inner retaining ring 19 (and, as the case may be, the retaining ring18) is also complemented by a rubber seal 3. This is preferably aso-called lip seal having a positive radius towards the pumped medium,allowing the pumped medium to aid in pressing the seal 3 against theshaft 22. Thus no pocket is created here either, as opposed toconventional O-ring seals.

The seal rings 1 and 2, 2′ themselves are preferably manufactured from ahard material, such as silicon carbide. Furthermore, they preferablyhave a diamond coating on the sealing surfaces. The diamond coatingreduces the friction to a third of that of normal sealing materials,entailing lower heat generation and allowing the seal to handle dryfriction. The coating also has a high wear resistance. Thus, the sealingrings can handle a higher closing force.

The single seal according to the present invention thus fulfils exactingdemands on dimensions, hygiene and balancing degree. The invention hasbeen described in detail with reference to a preferred embodiment asillustrated in the drawings. A person skilled in the art will understandthat dimensions, selected materials, etc. can be varied withoutdeparting from the scope of the invention. The mechanical connectionswith screws, pins and similar may be varied in many ways. The inventionis only limited by the following claims.

1. A single seal assembly for the sealing of a rotary shaft extendingthrough a wall of a housing and, seal off a chamber inside the housingfrom outside the wall, said seal assembly comprising a flange adapted tobe mounted on the wall, an outer sealing ring and an inner sealing ringdisposed on the shaft within the chamber inside the housing, saidsealing rings being in sliding and sealing contact with each other, theouter sealing ring being fastened to the flange, the inner sealing ringsurrounding said shaft and being secured to an axially extending member,said axially extending member being fastened with and rotating with theshaft, and extending through the flange into the chamber, wherein theaxially extending member is subjected to pressure in said chamber forproducing a pulling force acting in a direction to pull the inner ringagainst the outer ring to increase contact between the sealing ringswhile developing a torque to drive the inner sealing ring with saidshaft in common rotation, wherein said axially extending member is aslitted sleeve which comprises circular segments connected to each otherby lands, said lands being alternately located so that the sleeve iselastically extendable.
 2. A single seal assembly according to claim 1,wherein two said lands are provided between each segment, the landsbeing located opposite each other at 180° in one pair and at 90° to thelands in alternate pairs.
 3. A single seal assembly according to claim1, wherein a number of lands are evenly distributed around thecircumference of the sleeve and alternately in every second pair.
 4. Asingle seal assembly according to claim 1, wherein the number ofsegments is in the range of 1–10.
 5. A single seal assembly according toclaim 1, wherein the sleeve is connected to the inner sealing ring bymeans of a lug at the edge of the sleeve, said lug engaging a recess inthe inner sealing ring.
 6. A single seal assembly according to claim 1,wherein the sleeve is connected to the shaft by means of a stop screw.7. A single seal assembly according to claim 1 wherein the outer sealingring is brought against the flange with a first further sealtherebetween, and the inner sealing ring is brought against the shaftwith a second further seal therebetween.
 8. A single seal assemblyaccording to claim 7, wherein the second further seal between innersealing ring and the shaft is a lip seal.
 9. A single seal assemblyaccording to claim 1, wherein the axially extending member ismanufactured from a rolled metal sheet.
 10. A single seal assemblyaccording to claim 1, wherein the sealing rings are manufactured fromsilicon carbide with a diamond coating on the contact surfaces.
 11. Asingle seal assembly for the sealing of a rotary shaft extending througha wall of a housing and seal off a chamber inside the housing fromoutside the wall, said seal assembly comprising a flange adapted to bemounted on the wall, an outer sealing ring and an inner sealing ringdisposed on the shaft within the chamber inside the housing, saidsealing rings being in sliding and sealing contact with each other, theouter sealing ring being secured to the shaft for rotation therewith theinner sealing ring surrounding said shaft and connected to an axiallyextending tension coil spring, said axially extending coil spring havingan outer end fastened to said outer sealing ring and rotating with theshaft, said coil spring having an inner end secured to said inner ringand producing a pulling force acting in a direction to pull the innerring against the outer ring to increase contact between the sealingrings while developing a torque to drive the inner sealing ring inrotation with said shaft, wherein the inner sealing ring is providedwith an internal groove following the pitch of the spring, said springbeing threaded in the groove and ending with a straight axially directedpart engaging a recess in the sealing ring, and the outer end of thecoil spring is attached to an outer retaining ring secured to the outersealing ring, said outer retaining ring being provided with an internalgroove following the pitch of the spring, the spring being threaded inthe groove and ending with a straight axially directed part engaging arecess in the outer retaining ring.
 12. A single seal assembly accordingto claim 11, wherein the outer retaining ring is connected to the shaftby means of a stop screw.
 13. A single seal assembly for the sealing ofa rotary shaft extending through a wall of a housing and, seal off achamber inside the housing from outside the wall, said seal assemblycomprising a flange adapted to be mounted on the wall, an outer sealingring and an inner sealing ring disposed on the shaft within the chamberinside the housing, said sealing rings being in sliding and sealingcontact with each other, the outer sealing ring being secured to theshaft for rotation therewith, the inner sealing ring surrounding saidshaft and connected to an axially extending tension coil spring, saidaxially extending coil spring having an outer end fastened to said outersealing ring and rotating with the shaft, said coil spring having aninner end secured to said inner ring and producing a pulling forceacting in a direction to pull the inner ring against the outer ring toincrease contact between the sealing rings while developing a torque todrive the inner sealing ring in rotation with said shaft, wherein theinner end of the coil spring is attached to the inner sealing ring bymeans of a retaining ring, which is provided with an internal groovefollowing the pitch of the spring, the spring being threaded in thegroove and ending with a straight axially directed part engaging arecess in the retaining ring, and the outer end of the coil spring isattached to an outer retaining ring secured to the outer seal ring, saidouter retaining ring being provided with an internal groove followingthe pitch of the spring, the spring (8) being threaded in the groove andending with a straight axially directed part engaging a recess in theouter retaining ring.